Loudspeaker apparatus



April 11, 1961 s. CARLSSON LOUDSPEAKERAPPARATUS Filed Sept. 27, 1954 m J LL.

United States LOUDSPEAKER APPARATUS Stig Carlsson, Holbrsgaten 168 Stockholm-Bromma, Sweden Filed Sept. 27, 19 54, Ser. No. 458,650

Claims priority, application Sweden Oct. 2, 1953 12 Claims. (Cl. 18131) It is known that it is diflicult to realize a good loudspeaker reproduction of the entire audio spectrum. The difficulties may be divided into two groups: the one group concerning the question of generating the acoustic power required without introducing distortion, which is most difficult at the lowest audio frequencies; the other group concerning the question of having the generated acoustic power evenly distributed to the listeners in the listeningroom, which is difficult at low and high audio frequencies.

The present invention concerns the distribution of the sound from the loudspeaker but it also influences the generation of the sound by increasing the acoustic efficiency of the loudspeaker at low audio frequencies.

It is an object of the present invention to provide a loudspeaker having throughout the audio frequency spectrum a transmission to the ears of the listener as far as possible independent of the location and direction of the head of the listener in the listening-room.

Another object of this invention is to increase the acoustic eflicienoy of the loudspeaker at low audio frequencies.

Still another object of the invention is to obtain the two aims above, without bulky arrangements, simply by making the loudspeaker use the characteristics of the listening-room efficiently.

The subject of this invention is the configuration of the loudspeaker apparatus as regards the location and direction of its sound-radiating surfaces. The principle of the invention is to make the loudspeaker such that it uses the adjacent surfaces of the listening-room (wall or walls, floor and/or ceiling) as integral parts of the loudspeaker system in such a way that the following two effects are achieved:

1) At low audio frequencies reflected sound-waves from the adjacent surfaces of the room are added substantially in phase to the direct sound-wave from the loudspeaker, and

(2) At high audio frequencies, besides the direct soundwave from the loudspeaker, reflected sound-waves from the adjacent surfaces of the listening-room arrive at the listener from different directions.

A preferred embodiment of the invention comprises a loudspeaker assembly comprising two or more sound radiating units of which at least one radiates a low frequency range, and at least one radiates a high frequency range. Each unit may include one or more loudspeaker mechanisms or resonator ports. Alternatively the high frequency unit may also include a reflector arrangement.

The assembly is so designed that the sound radiating units are horizontally displaced relative to each other and that the apparatus may be placed in such a relation to adjoining surfaces of the enclosure or listening-room, that the center of radiation of the low frequency radiating stem ice

unit is located close to said room surfaces while the center of radiation of the high frequency radiating unit is located at a greater distance from said room surfaces, and radiates in different directions. Thus at high frequencies a listener receives at least one reflected soundaudio frequency radiating unit to that room surface; if

the apparatus comprises a reflector arrangement the distance from said high frequency radiating unit is to be measured via the center of gravity of the reflector sur face.

At low frequencies the reflected sound pressure waves from the adjoining surfaces of the room, added in phase or near in phase to the direct sound pressure from the loudspeaker, increase the acoustic efficiency of the loudspeaker. At high frequencies, due to the reflections from the adjacent surfaces of the room, the listener, in addition to the direct sound from the loudspeaker, receives sound from directions other than that of the direct sound and of almost the same intensity.

The distance between low frequency sound radiating units and high frequency sound radiating units, inherent in the sound reproducing apparatus of the present invention, can be made rather great, and yet the unity of the sound source impression is well preserved.

At low frequencies, sound radiating surfaces or openings of usual dimensions are omnidirectional. Locating the radiating surfaces or openings of the low frequency sound radiator close to adjacent boundary surfaces of the listening-room increases the acoustic efficiency of the radiator and results in a smoother propagation of the sound because the reflected sound from said adjacent boundary surfaces of the listening-room is added in phase or near in phase to the direct sound. If said low frequency radiating surfaces or openings are close to one boundary surface or close to two or three boundary surfaces at right angles to each other, each of said boundary surface or surfaces will increase the mechano-acoustic efliciency of the radiator (from mechanical to acoustical energy) and the electro-acoustic efficiency of the radiator (from electrical to acoustical energy). The upper limiting frequency of these effects will be higher the shorter the distance between said radiating surfaces or openings and the adjacent surfaces of the room. Said limiting frequency may easily be raised above 200 c.p.s., and in some cases it may be raised above 500 c.p.s.

At high frequencies, the Wave-length of sound is of the same order or less than the dimensions of the sound radiating surfaces and the head of the listener. This causes the radiation of the sound radiating surfaces to be directed, and it also affects the hearing of the listener because the intensity of the sound pressure varies around the head of the listener due to the sound field disturbance of the head. The directivity of the sound radiating surfaces is reduced by using a plurality of sound radiating surfaces oriented in different directions. Such directivity is reduced still more if the radiation from said high frequency sound radiating surfaces is reflected at the adjacent surfaces of the room, thus increasing the effective number of sound radiating surfaces due to image phenomena. Both measures contribute to a more uniform distribution of the sound energy radiated. By locating these high frequency sound radiating surfaces at some distance spaced from each other, and the listener will receive the sound radiation from different directions. This reduces the directivity of the listeners aural sensation.

It is known that at frequencies above 1000 c.p.s the reflection and diffraction of sound around the head of the listener causes intensity differences at his two ears up to as much as 20 db or more, and when the listener turns his head, his cars will receive intensity variations of the same order. Auditory localization at high frequencies is due to this phenomenon. In the case of live music high frequency producing musical instruments will transmit to the listener the high frequency sounds not only direct but also my way of reflections at the surfaces of the room, e.g. the listener gets the sound from different directions. In a good concert-hall the sound arrives at the listener from many different directions too. However, loudspeakers of conventional design send high frequency sounds only forwardly toward the listener, and not also toward the adjacent surfaces of the room. From these adjacent surfaces, thus, only weak and negligible secondary reflections, previously reflected at other walls of the room, arrive at the listener. The inventor considers this type of high frequency distribution a reason for the impression, described by many writers, that the sound from a loudspeaker seems to come from a small opening in a wall.

Investigations indicate that the effect of the high frequency distribution according to the invention is that the sound intensity variations around the head are less where the sound energy consists of the sum of the direct sound and the differently directed reflections of about the same intensity than where the sound energy consists of the direct sound only.

Further and more limited objects of the invention will be pointed out hereinafter and will be realizable in and through the construction and arrangement of parts shown in the drawing hereof, wherein Fig. 1 is a perspective view of a loudspeaker apparatus. Fig. 2 shows the external bottom surface of said apparatus. Fig. 3 is a perspective view of another loudspeaker according to the invention.

The loudspeaker assembly shown in Figs. 1 and 2 is in tended for high fidelity reproduction of the frequency range 25 to 20,000 c.p.s. The casing 1 of the apparatus has the shape of a truncated cone, which shape has been found especially suitable. A plate 24 closes the larger end thereof. The loudspeaker may be placed on the floor (or alternatively mounted upside down 'on the ceiling) either in a corner or at a wall, with the axis of the body tilted, pointed out from the corner or the wall. The casing 1 is provided with legs 2 which maintain the bottom surface 24, shown in Fig. 2, spaced from the floor. Most of the casing is occupied by the low frequency generating unit of the loudspeaker assembly with its sound radiating elements, the openings 3 and 4, located in the bottom surface 24 of the casing. In the opening 3 a loudspeaker mechanism 3' is mounted and the opening 4 is the port of a resonator cooperating with said mechanism and located in the lower part of the casing. This unit of the loudspeaker assembly is mainly used for low frequencies up to 200 or 500 c.p.s. Higher frequencies are reproduced by a high frequency unit comprising a loudspeaker mechanism 5 mounted in the top of the casing 1. At frequencies where the sideward radiation of this loudspeaker mechanism 5 ceases, a second high frequency unit comprising a plurality of small loudspeaker mechanisms 6, '7, S and 9 take over the function.

The tilted axis of the casing provides the desired horizontal displacement of the low and high frequency units with respect to each other.

Another embodiment of the inventon, using only one loudspeaker mechanism for the whole frequency range reproduced, is shown in Fig. 3. The main body of the apparatus consists of a cylindrical casing 10, the axis of which is arranged in vertical position. The casing 10 is provided with a coverll and a bottom wall 12. A sound emitting surface or opening 13 in the cover emits as well high frequencies as medium and low frequencies, i.e. the whole frequency range. Above said opening 13 of the apparatus is provided a reflector 14, coaxal with the opening 13. The reflector, which is connected with the casing 10 by means of rods, 15, is adapted to reflect high frequencies in horizontal directions. Low frequencies are emitted through an opening 16 communicating with the casing 10 by means of a tube 17 forming part of an acoustic rmonator for said low frequencies. According to the example shown the tube 17 serves as a carrying arm for the casing 10 and is provided with mounting means so that the whole apparatus can be mounted on a wall 18.

It is evident that the apparatus can be mounted in any other way, e.g. on a tripod, but it is significant that the distances between the wall or the walls of the room and the opening 16 and the reflector 14 are maintained at the same proportions as shown in Fig. 3. V

A consequence of the invention is that it enables the adjacent reflecting surfaces of the listening-room to exert a predictable effect upon the transmission characteristics that can be considered when designing the sound reproducing apparatus. Thus the sound that arrives at the listener from the loudspeaker and those sunfaces of the room that are adjacent to the loudspeaker can be made in close replica of the input signal. At low frequencies where no directional variations in sound pressure arise at the ears of the listener, the fact that the loudspeaker radiates close to adjacent boundary surfaces of the listening-room causes the reflected sound from those surfaces of the room to be added in phase to the direct sound to provide an increased efficiency of low frequency transmission independent of the frequency variations within the low frequency range.

At high frequencies where directional variations in sound pressure occur at the ears of the listener, the fact that the loudspeaker radiates more distantly from said room surfaces and almost omnidirectionally reduces these variations, and at the same time provides a more uniform energy distribution in the listening-room.

Having thus described my invention, what I claim is:

l. A loudspeaker cabinet comprising a substantially frusto-conical casing having a plate closing the larger end thereof, said plate having a loudspeaker opening and a resonance port therein, the smaller end of said casing providing an opening for the reception of a loudspeaker, said casing having at least one loudspeaker opening in the side thereof adjacent its smaller end, and supporting legs attached to the larger end thereof for supporting said casing at a desired location on a floor.

2. A loudspeaker cabinet as claimed in claim 1 having three legs, at least one leg being longer than another for supporting said casing in a tilted position whereby when said casing is located in the corner of a room and tilted away from said corner, said side opening can be spaced from a wall of said corner by a greater distance than the loudspeaker opening in said plate.

3. A loudspeaker cabinet as claimed in claim 1 having four openings in the side thereof adjacent its smaller end, said openings being spaced substantially equidistantly from each other around the 360 of the periphery of said casing side so as to accommodate a plurality of loud speakers facing in different directions.

4. A loudspeaker cabinet as claimed in claim 1 in which said opening in said smaller end is larger than said side opening so as to accommodate a loudspeaker of greater size than that accommodated in said side opening.

5. A loudspeaker cabinet comprising a substantially frusto-conical casing having a plate closing the larger end thereof, said plate having a loudspeaker opening and a resonance port therein, the smaller end of said casing providing an opening for the reception of a loudspeaker, said casing having several loudspeaker openings in the side thereof adjacent its smaller end, said openings facing in different directions, and three supporting legs attached to the larger end thereof which at least one leg is longer than another for supporting said casing in a tilted position at a desired location on a floor, whereby whensaid casing is located in the corner of a room and tilted away from said corner, the sound emanating from at least two of said side openings will be directed toward those two walls of the room, the intersection of which form said corner.

6. A loudspeaker cabinet comprising a substantially tubular casing having a plate closing one end thereof, said plate having a loudspeaker opening and a resonance port therein, the opposite end of said casing providing an opening for the reception of a loudspeaker, said casing having at least one loudspeaker opening in the side thereof adjacent said opposite end, and supporting legs attached to said casing adjacent said first mentioned end thereof for supporting said casing at a desired location on a floor.

7. A loudspeaker assembly for use in an enclosure having at least one substantially vertical wall and a floor, said assembly including at least two units having high and low frequency ranges respectively, the centers of radiation of said units, respectively, being displaced vertically and horizontally with respect to each other whereby said low frequency range unit may be placed closer to the floor and wall than said high frequency range unit.

8. A loudspeaker assembly as claimed in claim 7 in which the extent of said horizontal displacement of said units is substantial with respect to the distance between said low frequency range unit and said vertical Wall when said low frequency range unit is located sufliciently close to said vertical wall that the reflected sound pressure waves from said vertical wall will be added in phase or near in phase to the direct sound pressure waves from said low frequency range unit, whereby the center of radiation of said high frequency range unit may be spaced from said vertical wall by a distance which exceeds 1.6 times the distance between said vertical wall and the center of radiation of said low frequency range unit.

9. A loudspeaker assembly as claimed in claim 7 in which the radiation from said high frequency range unit is sufliciently omnidirectional as to cause a substantial portion of the high frequency radiation to be transmitted into said enclosure by reflection from said vertical wall when said high frequency range unit is located near said vertical wall, whereby said transmission by reflection will occur in a variety of directions.

10. A loudspeaker assembly as claimed in claim 7 which includes two units having high frequency ranges, one of said units comprising a loudspeaker mechanism which exhibits sideward radiation, and the other of said units comprising a plurality of smaller loudspeaker mechanisms which are oriented in different directions.

11. A loudspeaker assembly as claimed in claim 7 in which said high frequency range unit comprises a plurality of loudspeaker mechanisms oriented in dilferent directions so that a substantial portion of the high frequency radiation will be transmitted into said enclosure by reflection from said vertical wall when said high frequency range unit is located near said vertical wall.

12. A loudspeaker assembly as claimed in claim 7 in which said high frequency range unit comprises a loudspeaker mechanism which exhibits sideward radiation.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Publication, R. Doby et al., Radio and Television News, November 1949, pages 54, 55, 56, 118, 130. 

